Materials having a high dielectric constant (k) may be used for a thin film in a semiconductor device such as a gate insulation layer of a MOS transistor, a dielectric layer of a capacitor or a dielectric layer flash memory device. The thin film including a high-k material may have a thin equivalent oxide thickness (EOT) and/or may reduce the leakage current between a gate electrode and a channel, or between a lower electrode and an upper electrode. The thin film may also improve the coupling ratio of the flash memory device.
Examples of a high-k material may include tantalum oxide (Ta2O5), yttrium oxide (Y2O3), hafnium oxide (HfO2), zirconium oxide (ZrO2), niobium oxide (Nb2O5), barium titanium oxide (BaTiO3), strontium titanium oxide (SrTiO3) and the like. Hafnium oxide (HfO2) has been used as a material for forming a thin film having a high dielectric constant. For example, U.S. Pat. No. 6,348,386 to Gilmer discusses a method of forming a thin film using hafnium oxide (HfO2). However, since the dielectric constant of a hafnium oxide layer is about 20, the hafnium oxide layer may be less desirable for manufacturing a semiconductor device that requires a dielectric constant greater than 20.
Accordingly, a thin film including zirconium oxide instead of hafnium oxide has been employed. The zirconium oxide layer has a dielectric constant of about 30 and a decreased equivalent oxide thickness. A method of forming a thin film including zirconium oxide is discussed in U.S. Patent Application Publication No. 2004/0033698 and U.S. Patent Application Publication No. 2002/0190294. However, since the dielectric constant of the zirconium oxide layer is about 30, the zirconium oxide layer may not be suitable during fabrication of a semiconductor device that requires a dielectric constant of over 30. Thus, a thin film including titanium oxide and having a dielectric constant of about 60 has been employed for fabrication of highly integrated semiconductor devices. However, titanium oxide may have a relatively lower bonding energy than hafnium oxide or zirconium oxide so that the titanium oxide layer may have undesirable leakage current characteristics.
To address some of the foregoing issues, a thin film including zirconium titanium oxide (i.e., simultaneously including titanium oxide and zirconium oxide) has been developed. The thin film including zirconium titanium oxide may exhibit desirable leakage current characteristics in comparison with a conventional titanium oxide layer and/or may possess a relatively higher dielectric constant that is the same as, or similar to, that of a conventional titanium oxide layer.
A method of forming a thin film including zirconium titanium oxide is discussed in U.S. Patent Application Publication No. 2002/0190294 and Korean Laid-Open Patent Publication No. 2004-062243. Specifically, a method of forming a thin film using ZrCl4 as a zirconium source and TiCl4 as a titanium source is discussed in U.S. Patent Application Publication No. 2002/0190294. A method of forming a gate insulation layer having a multi-layered structure that includes a first film of zirconium oxide and a second film of titanium oxide is discussed in Korean Laid-Open Patent Publication No. 2004-062243. However, a thin film having a single layer structure that includes zirconium titanium oxide and a method of forming this thin film are not discussed in U.S. Patent Application Publication No. 2002/0190294 or Korean Laid-Open Patent Publication No. 2004-062243.